Construction joints refer to the joints formed between pre- and post-concrete concretes due to design requirements or construction needs to be poured in stages during the concrete placement process. Therefore, the construction joint is not real, it is because the post-cast concrete exceeds the initial setting time, and there is a joint surface with the concrete that is poured first. This joint surface is called a construction joint. The following small series introduces the function of construction joints and the processing requirements of construction joints.
The role of construction joints
Construction joints can accurately grasp the specific implementation of grades (or segmented construction) and can effectively guarantee the construction quality of buildings. In general, construction joints need to be reserved before the construction. Planning ahead where specific construction joints are reserved can make the building not appear to be insecure between the parts due to the division of construction. problem. When we reserve the construction joints, we need to calculate how long it takes for each segment to solidify the concrete, and then determine a reasonable time difference so that each part can be constructed in sections and firmly combined. This is the effect of construction joints and the significance of construction joints.
Construction joint indwelling position
1. Construction joints shall be placed under the top of the foundation, below the girder or crane girder leg, above the crane girder, below the column caps of the beamless floor.
2, and the floor slab into an overall large cross-section beam, construction joints should be placed in the bottom of the board 20 ~ 30mm below. When there is a beam under the board, stay in the lower part of the bracket.
3. For unidirectional plates with an aspect ratio greater than 2, the construction joints shall be placed at any position parallel to the short side of the plate. At the same time, the construction joints shall be left in a vertical position.
4. The slab with primary and secondary beam should be poured along the direction of the secondary beam. Construction joints should be placed within the middle 1/3 of the secondary beam span.
5. The construction joints on the wall shall be left in the middle 1/3 of the crossing span of the door opening, and may also be left at the intersection of the vertical and horizontal walls.
6. The construction joints on the stairs should stay at 1/3 of the tread board. The concrete of the stairs should be poured continuously. If it is a multi-story staircase and the upper floor is a cast-in-place floor slab and is not poured, the construction joint can be left in place; it should be left at 1/3 of the middle of the stair section, but pay attention that the joint surface should be perpendicular to the axis of the staircase. direction. (The reason for the dispute in construction is that the old code stipulates that the stair construction joints must be placed in the middle 1/3 section, and the traditional construction is left at the upper and lower 3 steps, and when it is placed in the middle of the ladder section, the shear force is theoretically smaller. However, the quality of the construction joints during construction is not well controlled, and it is easy to produce a short-time “overhang†at the time of the secondary formwork, which is not conducive to the quality control of the components.
7. The construction joints of the pool pool wall should be left on vertical walls 200 to 500 mm above the floor surface.
8, two-way force floor, mass concrete, arch, shell, warehouse, equipment foundation, multi-layer rigid frame and other complex structures, construction joints should be set according to design requirements.
Construction joint processing requirements
1. When old concrete surfaces and exposed steel bars (pre-embedded parts) are exposed to cold air, deal with old concrete within 1.5m from new and old concrete construction joints and exposed steel bars (embedded pieces) with a length of 1.0m. ) Carry out cold insulation.
2. When the concrete does not need heating and curing, and does not freeze during the prescribed curing period, the concrete may be poured directly for non-frost ground or old concrete surfaces.
3. When the concrete needs to be heated and cured, the temperature difference between the newly cast concrete and the adjacent hardened concrete or geotechnical medium shall not be greater than 15°C; the temperature of the ground surface in contact with the concrete shall not be lower than 2°C. 11.3.11 The temperature at the start of concrete curing shall be determined by thermal calculation according to the construction plan, but shall not be less than 5 °C, and the thin section structure shall not be less than 10 °C.
4. The cement mortar and loose layer on the surface of the poured concrete should be removed. The area of ​​fresh concrete exposed after cutting the hair should not be less than 75%. When cutting hair, the concrete strength should meet the following requirements:
1) When using artificial cutting hair, not less than 2.5MPa.
2) When cutting with a wind motive or other machinery, it is not less than 10 MPa.
5. The concrete surface treated by the chiseling process should be flushed with water, but there should be no accumulation of water. Before pouring new concrete, a layer of cement paste should be brushed on the old concrete surface for vertical construction joints. For horizontal construction joints, a layer of glue with a thickness of 10mm~20mm, which is slightly smaller than that of concrete, should be laid on the surface of old concrete. For a cement mortar with a sand ratio of 1:2 or a layer of concrete about 30 cm thick, the coarse aggregate should be reduced by 10% compared to the newly cast concrete.
6. When the construction joints are sloped, the old concrete shall be cast or cut into steps.
Editor's summary: The function of construction joints and the processing requirements for construction joints are introduced here. I hope to be helpful to everyone. If you want to know more about yourself, you can follow the information on this site.
Construction, installation, renovation, construction knowledge, construction, bottom, construction contract, construction joint, function
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